Currently, converters, Static Var Generators (SVG), and wind power systems, etc. with a higher voltage level (such as 35 kV) usually adopt a topology of cascaded power conversion modules. For example, when a grid side of the topology is directly connected with a grid, and a load side of the topology is connected with a motor through an inverter, the topology is a converter; when the grid side of the topology is directly connected with the grid, and there is no load on the load side, the topology is an SVG; when the grid side of the topology is connected with a generator, and the load side of the topology is connected with the grid through a module, the topology is a wind power system; and when the grid side of the topology is connected with the generator, and there is no load on the load side of the topology, the topology is the SVG. A controller of each power conversion module needs a power supply, so how to get the power supply is very important. The present disclosure is to solve a problem with respect to taking power.